L. J. Gallego

A molecular dynamics study of the evaporation of small argon clusters

Abstract Using constant energy molecular dynamics simulations, we have studied the evaporation of atoms from most of the Lennard-Jones clusters in the size range N=11–20. It is found that, for a given evaporation rate, the 13- and 19-atom clusters need greater kinetic energy for an atom to be evaporated than the clusters of neighbouring sizes, i.e. they are more stable (“magic number” behaviour). We have also calculated the binding energies of the evaporated atoms for the neutral clusters studied; the results are compatible with available information for ionized argon clusters, although detailed comparison between results for neutral and ionized inert gas clusters is highly non-trivial.

Theory of the thermodynamic properties of binary mixtures of organic molecules with size mismatch

Abstract The Flory expression for the Gibbs free energy of mixing of a binary mixture is improved by introducing a hard-sphere form for the entropy of mixing. The resulting expression is used to describe the characteristic features of organic mixtures of globular molecules with size mismatch. In particular, we show that the above model, with an interchange energy depending on temperature, accounts for the thermodynamic properties and concentration fluctuations of a number of octamethylcyclotetrasiloxane-based mixtures.

Glass formation in the Cu–Ti–Zr system and its associated binary systems

Abstract The model we have previously used to predict the glass-forming range of binary transition-metal alloys is extended to ternary systems. As in the binary case, the treatment combines classical elasticity theory and Miedemas model for the heat of formation of alloys, and takes into account the factors which are recognized as most influencing glass formation, specifically the valency, the electro-negativity and the atomie size mismatch. As an application of the theory, we study the amorphization of the Cu–Ti–Zr system and its associated binary systems, for which the influence of working conditions on the glass-forming range is examined.

Possibility of spontaneous vitrification in Ti-Cr alloys

Abstract Comparison of their calculated free energies shows that in Ti-Cr systems the Cr-based bcc solid solution is more stable than the amorphous phase at the temperatures of interest. This means that spontaneous vitrification (SV) cannot take place by annealing of the perfect bcc solution. An imperfect, highly distored bcc solid solution is required as the starting material for SV in this system.

On the Concentration Dependence of the Ordering Potential in Liquid Li-Pb Alloys

Abstract By using the Gibbs-Bogoliubov variational method, Bhatia and Young have recently provided an improvement on the Flory model of mixtures. The expression for the free energy of mixing arising from the Bhatia and Young approach is used to study the concentration fluctuations Scc (0) of the liquid Li-Pb alloy. It is shown that the experimental behaviour of Scc (0) can be explained within the framework of this theory if the ordering potential is assumed to vary strongly with concentration near the stoichiometric composition Li4Pb.

A hard-sphere description of the thermodynamic properties of binary mixtures of organic molecules

Abstract The Flory expression for the Gibbs free energy of mixing of a binary mixture, improved by introducing a hard-sphere form for the entropy of mixing, accounts succesfully for the thermodynamic mixing functions and the concentration fluctuations of organic mixtures of globular molecules. In particular, the use of an interchange energy depending on temperature through an expression proposed by Kehiaian allows a good description of the variation of these properties with temperature in the systems 2,3-dimethylbutane+cyclohexane, +cycloheptane and +cyclo-octane.

Concentration dependence of the heat of formation of binary liquid alloys

Abstract A link is established between Miedemas work on heats of formation of metallic alloys and a theory of mixtures that is essentially a version of Guggenheims quasichemical model in terms of contact surface interactions. The theory in question, which has been developed by Kehiaian and applied to organic mixtures, allows a rational derivation of the dependence of the heat of formation of liquid alloys on their composition. The interchange energy, which appears in this theory as a parameter to be fixed experimentally, can be obtained through Miedemas treatment in terms of the electronegativities and the boundary electron densities of the pure metals.

Concentration Fluctuations in Binary Mixtures of Inert-Gas Fluids

Abstract The non-random two-liquid theory developed by Renon and Prausnitz has been used to study the concentration fluctuations in binary Ar-Kr and Kr-Xe liquid mixtures. The concept of local composition on which this theory is based is very helpful in interpreting the tendency for phase separation exhibited by both systems.

Prediction of Metastable Alloy Formation and Phase Transformations Induced by Ion Bombardment in Binary Metal Systems

Thermodynamic aspects of the formation of metastable alloys by ion bombardment, and phase transformations, are analysed using a model which combines classical elasticity theory and Miedema’s model of heats of formation of alloys. This model has recently been used successfully to predict the glass forming ranges of binary and ternary transition metal alloys.

Description of Scc (0) in Liquid NaCs Alloys using The Bhatia-Young Model of Mixtures

Abstract The Bhatia-Young expression for the free energy of mixing of a binary fluid has been used to study the concentration fluctuation in liquid NaCs alloys. This system has a strong tendency to homocoordination at sodium concentration near 0.8. In spite of this fact, good overall agreement with the experimental Scc (0) data is provided by assuming an ordering potential which is independent of concentration.